Comment by WhyNotHugo

Regular domestic connections often block ports (especially email). In many countries, ISPs won't sell you a static IP (your dynamic address might not change ever, but you don't control rDNS records).

These kind of measures force people to move onto a rented server instead. Often ISPs rent servers themselves. The conflict of interest here is hard to ignore: if ISPs make it easy and convenient to host from home, their business of renting servers suffers.